TUESDAY, April 27 (HealthDay News) -- The anticipated approval this week of a therapeutic prostate cancer vaccine by the U.S. Food and Drug Administration could be a milestone against the disease and cancer in general, experts say.

The vaccine, called Provenge, appears to extend survival in men with advanced prostate cancer, and it does so without the serious side effects associated with chemotherapy, radiation and hormone therapy.

"It is certainly exciting to see a drug that has made it this far and appears on the threshold of approval," said Dr. J. Len Lichtenfeld, the deputy chief medical officer of the American Cancer Society.

The vaccine is not aimed at preventing prostate cancer in men who have not developed the disease, and it is far from a cure for those who have it, Lichtenfeld cautioned. "Provenge represents a modest advance in survival for patients with advanced prostate cancer, but the drug doesn't delay the progression of the disease," he said.

Still, it might prove possible to use Provenge in the earlier stages of prostate cancer, where it might be even more effective, Lichtenfeld said. "The hope is if a vaccine is effective in late-stage disease that it is going to be even more effective in the earlier treatment of that same disease," he said.

But that benefit would have to be shown in clinical trials, Lichtenfeld said.

"If it does get approved it will be groundbreaking." Lichtenfeld said. "It will represent a new treatment option. It will have a modest impact on prostate cancer survival, but it's small changes in treatments over time that add up to a major improvement. So I wouldn't be discouraged by what is a small increment in survival."

Provenge is a therapeutic (not preventative) vaccine that is made from the patient's own white blood cells. Once removed from the patient, the cells are treated with the drug and placed back into the patient. These treated cells then cause an immune response, which in turn kills cancer cells, while leaving normal cells unharmed.

Provenge was developed by Seattle-based Dendreon Corp., which conducted initial studies among men with advanced prostate cancer who had already failed standard hormone treatment. Among these men, the vaccine extended life by an average of 4.5 months, although some patients saw their lives extended by two to three years. The only side effects were mild flu-like symptoms, according to the study results.

In 2007, an FDA advisory panel recommended that the agency approve Provenge, but the FDA said more data was needed before it would approve the drug.

If the drug is approved, its use will most likely be limited to men with advanced prostate cancer. And at an expected cost of $75,000, it won't be inexpensive.

Dr. Mark Soloway, professor and chair of urology at the University of Miami Miller School of Medicine, said that "we certainly need the opportunity for our patients to have alternatives."

The big question, according to Soloway, is when do you use Provenge? Whether it should be used before chemotherapy or hormone therapy isn't clear, he said.

"There are problems with Provenge," Soloway said. "One is that it's very cumbersome, because patients have to provide their white cells, and I think that's on a regular basis. And two, it's likely to be very expensive."

Soloway agreed that Provenge might also be useful in earlier-stage prostate cancer, but studies are needed to prove that.

However, "once it's approved it's on the market and with proper informed consent you can use it for localized [early stage] prostate cancer. Whether insurance companies will pay for it is also not known," Soloway said.

Other new drugs to treat prostate cancer, such as Abiraterone, which prevents the production of the male hormone testosterone, are on the horizon and will compete with Provenge for new treatment regimens, he added.

According to American Cancer Society estimates, there are more than 192,000 new cases of prostate cancer diagnosed in the United States each year, and 27,360 men die from the disease.

Prostate cancer is the most common form of cancer diagnosed in American men, after skin cancer. More than 2 million American men who have had prostate cancer at some point are still alive today, and the death rate is going down, and the disease is being found earlier, according to the cancer society.